Radio frequency energy may be used to treat certain cardiac abnormalities, such as fibrillation, by ablating caridiac tissue. Radio frequency energy is delivered by RF generators in two phases: (i) the “ramp up” phase in which a relatively high amount of power is delivered to the ablating electrode until a desired set temperature is sensed by the thermocouple or thermistor, and (ii) the “regulation” phase in which power is still being delivered but regulated at a lower level to maintain the desired set temperature. This target temperature is predetermined by the operator, and is generally 50° to 55° C. for ablation of cardiac tissue.
Most RF generators have software modules which run simultaneously on portable computers during RF energy delivery to log the ablation episode. Typically, the parameters logged are sensed impedance, power delivered, as well as tissue temperature sensed by either thermistors or thermocouples. Currently, this information is typically used for post-procedural review.
The challenge in RF ablation of cardiac tissue is to create deep lesions in the cardiac tissue while avoiding coagulum formation. It follows that RF energy must be delivered efficiently into the tissue, and not delivered and lost into the blood medium. Current methods and systems are not adequate to assure that RF energy is delivered efficiently to cardiac tissue during an ablation procedure.
Prior studies in the delivery of RF energy have shown that when electrode-tissue contact is intermittent, the impedance value fluctuates and the power delivered also has to rapidly adapt in order to reach or maintain the target temperature. The rapid alternating impedance values therefore cause the output power waveform to also fluctuate rapidly. If the rise-time of the RF power waveform is sharp, and the noise modulated onto the RF source signal has high enough amplitude, it may be conducive for coagulum formation because it may undesirably approximate the coagulation waveform used by electro-surgical units. Therefore, there remains a need for systems and methods for performing RF ablation wherein effective contact with target cardiac tissue is assured to achieve deeper lesions and reduced coagulum formation.
The methods and systems of the current invention provide efficient delivery of radio frequency (RF) energy to cardiac tissue with an ablation catheter, thereby yielding consistently effective RF ablation procedures and improved patient outcomes.